The adsorption of lysozyme on the mesoporous molecular sieves MCM-41 and SBA-15 from buffered solutions with different pH values has been studied as a model protein adsorption system. The amount adsorbed depends on the solution pH as well as on the pore volume and the composition of the adsorbent. The adsorption isotherms at pH 6.5 to 10.5 fitted the Langmuir model (type L isotherm), while the isotherms recorded at pH 12 are of the S type. The maximum amount adsorbed was observed for AISBA-15 at pH 9.6 and amounted to 47.2,mumol/g (580 mg/g). The stability of SBA-15 toward to the buffer solution is higher for SBA-15 as compared to MCM-41, which is probably a consequence of the higher wall thickness of the former material. Diffuse reflectance Fourier transform infrared spectra of the adsorbed lysozyme confirm that the adsorption of the enzyme did not result in denaturation of Lz.